1. Field of the Invention
The present invention relates to a transflective liquid crystal display (LCD) device. More particularly, the present invention relates to a transflective LCD device having a reflection area and a transmission area for a liquid crystal (LC) layer, and adapted to be driven in an in-plane-switching (IPS) mode.
2. Description of the Related Art
LCD devices are roughly classified into a transmissive type and a reflective type in terms of the light used therein. Generally, transmissive LCD devices have a backlight source, and display an image by controlling the rate of transmission of the light emitted by the backlight source. On the other hand, reflective LCD devices have a reflection film and utilize the light reflected by the reflection film to display the image. Since the reflective LCD devices do not require any backlight source, the reflective LCD devices have an advantage over the transmissive LCD devices in terms of the power dissipation, thickness and weight of the device. However, since the reflective LCD devices utilize the ambient light as the light source thereof, the reflective LCD devices have a disadvantage in that the reflective LCD devices have a poor visibility in a dark environment.
Transflective LCD devices are known as a LCD device having both the advantages of the transmissive LCD devices and those of the reflective LCD devices (refer to Patent Publication JP-2003-344837A). The transflective LCD device has a transmission area and a reflection area in each pixel. The transmission area transmits the light from the backlight source disposed rear side of the LCD device and utilizes the backlight source as a display light source. The reflection area has a reflection film and utilizes the external light incident from the front side of the LCD device and reflected by the reflection film as a display light source. The transflective LCD device turns OFF the backlight source when it is situated in a bright ambient and displays the image by means of the reflection area to reduce the power dissipation of the LCD device. The transflective LCD device turns ON the backlight source when it is situated in a dark environment and displays the image by means of the transmission area so that it can clearly display the image in the dark environment.
The display modes of the LCD devices include the IPS mode as described above, which includes a lateral-electric-field drive mode and a fringe-field drive (FFD) mode. A LCD device adapted to operate in the IPS mode has a pixel electrode and a common electrode provided on the same substrate and applies an electric field to the LC layer in the lateral direction. The IPS-mode LCD device can realize a wider viewing angle compared to a twisted-nematic mode (TN-mode) LCD device by using a technique wherein the LC molecules in the LCD layer are rotated or turned in the direction parallel to the substrate.
Assuming that the IPS mode is adopted as the display mode for the transflective LCD device, there arises a problem in that the transmission area assumes a normally white mode if the reflection area assumes a normally black mode, whereby the image in the both areas is reversed. For a countermeasure of this problem, a technique for inserting a retardation film between a LC cell including the LC layer and a polarizing film has been adopted in the transflective LCD device (refer to non-patent publication-1: P-97: A Novel Transflective Display Associated with Fringe-Field Switching, T. B. Jung and S. H. Lee et al. [SID 03 DIGEST, 592], and non-patent publication-2: P-159: A Single Gap Transflective Fringe-Field Switching Display, E. Jeong, M. O. Choi, Y. J. Li, Y. H. Jeong, H. Y. Kim, S. Y. Kim and S. H. Lee [SID 06 DIGEST, 810]).
In the above technique, the slow axis of the inserted retardation film is arranged to have a significant angle with respect to a linearly-polarized light incident to the transflective LCD device. This arrangement results in a problem that the contrast ratio of the displayed image is degraded by deviation of the retardation value due to the range of variation in the thickness of the retardation film. There may arise another problem in that the viewing angle dependency of the retardation film degrades the viewing angle characteristic of the LCD device.